Introduction: Reduced miR-34a expression is associated with high-risk human papillomavirus (HR-HPV) infection and cervical cancer. Whether the reduction of miR-34a expression induced by HR-HPV E6 occurs in precancerous lesions, even before morphologic change, is still uncertain. Our study aimed to ascertain the possibility of pri-miR-34a involved in the development of cervical lesions and to explore the mechanism of altered pri-miR-34a expression induced by HPV-16 E6.
Methods: The levels of pri-miR-34a expression were examined in different cervical tissues, including normal cervical epithelium with (n = 32) or without (n = 32) HR-HPV infection, cervical intraepithelial neoplasia (CIN) with (n = 32) or without (n = 12) HR-HPV infection, and cervical cancer (n = 32), by semiquantitative reverse transcription-polymerase chain reaction. The HPV-16 E6 expression vector and HPV-16 E6 small interfering RNAs were conducted and transfected into 293T cells and SiHa cells, respectively. The expression of pri-miR-34a and p53 protein was simultaneously analyzed by reverse transcription-polymerase chain reaction and Western blot in cells with gene transfection and without.
Results: pri-miR-34a expression was significantly reduced in CIN and cervical cancer compared with normal cervical epithelium, as well as in CIN 2 and CIN 3 compared with CIN I. Moreover, the expression of pri-miR-34a was significantly lower in normal cervical epithelium and CIN with HR-HPV infection than in those without. Simultaneous down-regulation or up-regulation of pri-miR-34a and p53 expression was observed in E6-transfected 293T cells or E6 small interfering RNA-transferred SiHa cells compared with controls.
Conclusions: Reduced expression of pri-miR-34a occurs not only in cervical cancer but also in precancerous lesion even before morphologic change. The inhibition of miR-34a expression induced by HR-HPV E6 in the p53-dependent pathway is probably an early-onset event in the development of cervical cancer.